Method for producing explosive elements



s. HQ DAVIDSON 1:1- AL METHOD FOR PRODUCING EXPLOSIVE ELEMENTS Filed Sept. 12, 1955 5am-nel Hem* amas James Pez'cf v By' mi,

v www v ,47m/Mfrs METHOD FOR PRODUCING EXPLOSIVE ELEMENTS Samuel Henry Davidson, Largs, and Thomas James Reid,

f Ardrossan, Scotland, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Application September 12, 1955, Serial No. 533,907 i Claims priority, application Great Britain November 8, 1954 Claims. (Cl. 86-20) This invention relates to new and improved explosive elements for blasting under conditions of substantial hydrostatic pressure and in which the explosive charge comprises an ammonium nitrate blasting explosive.

v-Compressible ammonium nitrate blasting explosives, Vsuch asloosely packed ammonium nitrate powders of bulk densities' up to aboutV 1,3, comprising ammonium nitrate .and oxidisable ingredients, with if desired the addition kof other salts, in tinplate orsimilar thin sheet metal canisters when used under considerable hydrostatic pressuresv as in seismic prospecting or well blasting operations, fail to provide elective internal support for the canister in the blasting situation so that the canister may collapse sutiiciently to open its seams and thereby allow the inlet of water which may seriously reduce the eiiectiveness of the blast or may even cause the explosive to fail to explode.A Although it is possible to overcome this Adisadvantage with canisters of increased thickness and hence greater strength such canistersare not readily available, are considerably more'expensive Vthan those of the thicknesses normally used and make the explosive more difficult to initiate from outside the canisters. Another method of overcoming this disadvantage would be tov introduce the explosive charge under ypressure into they canister while suitably 'supporting the canister and wherein the pressure is of the order of that expected 1 to occur in use.

This method would require special machinery which would again add considerably to the cost and would increase the density of the explosive and would thusdecrease its sensitivity and so make it more diiiicult to Iinitiate from outside the canister.Y Methods havevalso been` proposed for preparing high density explosive `charges in a form adapted to iill readily into containers,

molten condition, maintaining in contacting relationship therewith adispersing agent and subsequently cooling andjsolidifying the resulting blend.

2 ammonium nitrate IV to ammonium nitrate III, i.e..32.3 C., is below the fusion point of any solid'fusible 'organic f sensitising agent which may be included in theexplosive,

The object of the present invention is to provide a more convenient method than heretofore for the production of explosive relements for use at a high hydrostatic pressure from a compressible ammonium nitrate powder explosive in a thin metal canister.

According to the present invention the method of producing explosive elements particularly suitable for use'athigh hydrostatic pressure comprises packing a charge of an ammonium nitrate powder explosive containingasmall amount of water, preferably not less than l0.1% and not more than 1.0% by weight of the ammonium nitrate, into a thin, for examp1e0.012 inch thick,v sheetmetal canister, subjecting the canister after sealing to such a temperature and for such a'period of y time'lthat at least the thin layer of the explosive which is closest to the sides of the canister attains a temperature which vis at least the transition temperature for and does not exceed 80 C., and thereafter allowing the canister to cool so thatthe ,explosive which is ,atA

least at said transition temperature is converted into hardened explosive.

Preferably the ammonium nitrate powder explosive contains at least 75% ammoniumnitrate.

The ammonium nitrate powder explosive may include to carry out the heating by total immersion in a` liquid, Y

preferably water, as this method is inherently safer vand also` enables the container to be simultaneously tested for leaks since any air inside will expand on vvheating and, if 'any leaks exist, will emerge as bubbles in the heating liquid.

For explosives containing ammonium nitrate whichl has not been treated with a crystal` habit modifier only a very small water content, e.- g. 0.1% by weightof the ammonium nitrate, is necessary whereas using explo,-v sives containing ammonium nitrate which has been treated with a crystal habit modifier a greater water content` with respect to the ammonium nitrate may be necessary.- With untreated ammonium nitrate the amount of water picked up from the atmosphere during handling-may often be enough. The water content should-never be sufficient to destroy the powder character of the composi-= tion at ordinary temperatures. The thickness of the hardened'layer desired will depend on the pressure the containeris required to withstand but" it is preferred that the explosive should be hardened throughout. The thickness of the layer of yhardened explosixe obtained will depend on the time to which the explosive is subjected to the heat treatment and on the temperature thereof. Thus for ammonium nitratecompositions in tins of diameter 2 inches immersed in water at C. immersion times of 1, 3. and 6A minutes give hardened layers of thickness 0, 0.5 and 0.8v cm.

respectively. e n

For lsaid tins containing ammonium nitrate compositions which are at a temperature of 19 C. before their immersion in the water at 70 C. the temperatures as recorded by thermocouples are at the end of one minute against the inside. wall 49.1 C. and 5 mm. 4fromvinside wall 24.4 C; at the end of 3 minutes against the inside wall 57.3 C., 5 mm. from inside wall 37V C., and 8 mm. from inside wall 25.7 C.; and at the end of 6 minutes `against the inside wall 61.1 C., 5 mm. from inside wall 45.7 C., 8 mm. from inside wall 34.5 C., and l5 mm. from inside Wall 23.7 C.

Temperatures of heatingfin the range-60H0 C'. are preferred since the times required in this yrange are reason; ably short and suitable for practical working. l Y 1 Y Referring to the drawing, Figure l shows apart section through an explosive element of the kind described in the specification, which has not been treated according the invention. whereby, as shown, a cylindrical layer S of the explosive adjacent to the sides of the canister 1 is converted into hardened explosive.

Figure 3 illustrates one method of carrying out the invention. `A canister 7 is submerged in a Water bath 9, provided with athermometer 11, and means for raising tlie'- temperature of the water by therequired amount, e. g`., a live steam pipe 13. The water bath could, of course, equally well contain any number of canisters and the orientation of the canisters in the water bath is. of no consequence.

As noted throughout the specification, the drawing illustr'ates only one embodiment of the invention, since, for example, the heating of the lled sealed canister may bev carried out by any convenient means.

The invention is illustrated by the following examples iri which all parts are by weight.

Example 1 An explosive composition is made by compounding together 90.0 parts of ammonium nitrate of particle size such that 100% by weight passes a No. 30 B. S. S. sieve, 98% passes a No. 60 B. S. S. sieve, 83% passes a No. 1'00 B. S. S. sieve, 70% passes a No. 120 B. S. S. sieve, 34% passes a No. 170 B. S. S. sieve and 7% passes a No. 240 B. S. S'. sievey and containing 0.05% by Weight of acidr magenta, 2.4 parts of water-wet nitrocellulose containing 662/ 3% by weight of nitrocellulose, and 7.6 parts of orthonitrotoluol. This composition is loaded into l lb. tins of diameter 2 inches on to which lids are sealed by a roll seam. A number of the canisters thus lledare submerged under 200 ft. of water at 15 C. for 1 hour after which only 65% of the tins re. All the tins collapse and 35% of the collapsed tins have leaks suicient to cause failure. A number of similarly iilled tins are immersed in hot water at 70 C. for 3 minutes and cooled. Upon examination some of these tins are found to have a hardened layer of' 0.5 cm. thickness against their walls. The unexamined tins are thereafter submerged under 200 ft. of water for l hour after which 95% fire. 95% of the tins show no signs of collapse before firing. The remaining have sufficient leaks, due for example to defective seaming, to cause failure.

Example 2 An explosive composition consisting of 92.5 parts ammonium nitrate of the same particle size as that used in Example 1 and containing 0.05% by weight acid magenta, 5.5 parts anthracite, 2 parts` orthonitroto-luol and 0.25 part water is packed loosely into 1 lb. tins of 2 inch, i; e. 50 mm., diameter which are sealed by roll seaming. The tins so charged are immersed in Water at 30 C., 34 C., 37 C. and 40 C. for one hour and subsequent to' cooling are cut open. The walls of these tins are 0.012 inch thick and are of tin plate. The `contents of the tins which are treated at 37 C. and 40 C. are set solid whereas the contents of the tins which are treated at 34 C. give only a thin layer of hardened explosive against the walls of the tins and those of the tins treated at 30 C. show no signs of being hardened. Further tests are then carried out by immersing tins so charged in water at 30 C. and 34" C. for 5 hours. Subsequent to cooling these tins are cut open. The contents of the tins which are treated at 34 C. are set solid Whereas those which are treated at 30 C. show no signs of being hardened.

With the thermocouples inserted at 0 mm., 5 mm., 8 mm., mm., and 25 mm. from the inside wall of the tins packed loosely with the above explosive composition which are at a temperature of 19 C. before they are irnmersed in water at the above mentioned temperatures of 34l C., 37 C. and 40 C. and by recording the temperaturesl at said distances at various time intervals it is found that when the water is at 40 C. at the end of 14 minutes 8 mm. from the inside Wall is 32.1 C. and 25 mm.

lil

21 (i. e. the centre) from the inside wall is 27.1 C.; at the end of 18 minutes 8 mm. from the inside wall is 33.2 C. an'd 25' mm. from the inside wall is 28.9 C.; and at the end of 24 minutes 25 mm. from the inside Wall is 32.3 C.; that when the Water is at 37 C. at the end of 18 minutes 8 mm. from the inside Wallis 31.5 C. and 25 mm. from the inside wall is 28 C.; at the end of 24 minutes 25 mm. from the inside wall is 30.2 C.; and at the end of 40 minutes 25 mm. from the inside wall is 33.0 C.; and that when the water is at 34 C. at the end of 22 minutes the inside wall is 32 C., 8 mm. from the inside wall is 30.3C. and 25 mm. from the inside Wall is 28 C.; and at the end of 60 minutes 25 mm. from the inside Wallis 32 C.

Example 3 two inch diameter 1 lb. tins made of 0.012 inch thick tinplate are lilled with an explosive containing 8% by weight trinitrotoluol, 88.5% by weight ammonium nitrate of the same particle size as in Example l and containin'gI 0.15% water, and' 3.5% by weight pulverised anthracite, made by milling the ingredients together in an edgel runner mill. The lids are scaled on by aV roll seam. The tins are thenheated overnight at 60 C. and after cooling are subjected'- to 1-30 lbs/sq. in. water pressure, i. e. 300 feet of water, for 20 hours. The tins show very little signs of collapse and only 2 tins fail to initiate from a No. 8 A. S. A. detonator. Tins which are lled with theA same: explosive composition and are not subsequently heat treated collapse and leak under 130 lbs/sq. in. water pressure so that initiation of the composition is impossible;

Example 4 An explosive composed of 91% by weight pulverised ammonium nitrate of the same particle size as in Example l containing 0.05 %l by Weight acid magenta, 0.15% Water, and 9% by weight orthonitrotoluene is made by. mixing the ingredients in a Werner Pfleiderer' type; mixer. 2 inch diameter 1 lb. tins made of 0.012 inch thick tinplate are filled with the explosive and the tins are then sealed by a roll seam. When the composition.l is set-hard, by heating overnight at 60 C. the tins show no signs of collapse under 1bs./sq. in. water pressure and the composition can be initiated by a No. 8 A. S. A. detonator in conjunction with a primer which is madefrom the explosive referred to in Example 3. Similarly filled tins which are not heat treated collapse and leak under this pressure of water.

Regarding theY nomenclature ammonium nitrate III and; I-V, respectively, ammonium nitrate IV is known in the art a's an ammonium nitrate having a crystal for-mf-which isv stable over the temperature range, 18 C.Y 'to 47.32 C. For ammonium nitrate III, the corresponding temperature range is +32 C. to +84 C.

What we claim is:

1-. A method of producing explosive elements particularly suitable for use at high hydrostatic pressure which comprises packing a charge of an ammonium nitrate powder explosive containing at least 75% by weight of ammonium nitrate IV and a small amount of water into ay thin sheet nieta-l' canister, subjecting the canister after sealing to such a temperature and for such a period of time that at least a layer of the explosive close to the sides of the canister attains a temperature which is at least the transition temperature for ammonium nitrate I'V to ammonium nitrate III, is below the fusion point of any solid fusible, organic sensitising agent which may be included in the explosive, and does not exceed 80 C and thereafter allowing the canister to cool so thatl the explosive which is at least at said transition temperature is converted into hardened explosive.

2. A method as claimed in claim 1 wherein the amount of water in the powder explosive is not less than 0.1%v and!` not more than 1.0% by weight of the ammonium nitrate.

'314A method as claimed. in claim 1 wherein the ammonium nitrate powder explosive .contains oxidising salts other than ammonium nitrate.

4. A method as claimed in claim 1 wherein the heat- -ing of the filled sealed canister is carried out by total immersion in a liquid.

5. A Amethod as' claimed in claim 1 wherein the temperature of heating for the canister after sealing is in the range 60 to 70 C. l

References Cited in the le of this patent UNITED STATES PATENTS 

1. A METHOD OF PRODUCING EXPLOSIVE ELEMENTS PARTICULARLY SUITABLE FOR USE AT HIGH HYDROSTATIC PRESSURE WHICH COMPRISES PACKING A CHARGE OF AN AMMONIUM NITRATE POWDER EXPLOSIVE CONTAINING AT LEAST 75% BY WEIGHT OF AMMONIUM NITRATE IV AND A SMALL AMOUNT OF WATER INTO A THIN SHEET METAL CANISTER, SUBJECTING THE CANISTER AFTER SEALING TO SUCH A TEMPERATURE AND FOR SUCH A PERIOD OF TIME THAT AT LEAST A LAYER OF THE EXPLOSIVE CLOSE TO THE SIDES OF THE CANISTER ATTAINS A TEMPERATURE WHICH IS AT LEAST THE TRANSITION TEMPERATURE FOR AMMONIUM NITRATE IV TO AMMONIUM NITRATE III, IS BELOW THE FUSION POINT OF ANY SOLID FUSIBLE ORGANIC SENSITISING AGET WHICH MAY BE INCLUDED IN THE EXPLOSIVE, AND DOES NOT EXCEED 80*C., AND THEREAFTER ALLOWING THE CANISTER TO COOL SO THAT THE EXPLOSIVE WHICH IS AT LEAST AT SAID TRANSISTION TEMPERATURE IS CONVERTED INTO HARDENED EXPLOSIVE. 